A lash is a sharp slap or strike with a rope or whip. In some parts of the world, lawbreakers receive a certain number of lashes as punishment for their crimes.
To deliver a lash is also to lash: "I instructed the jockey not to lash the horse," and another way to lash is to tie one thing securely to another. The part of a whip that actually connects with a person or animal's body is called a lash as well. When you lash out at someone, you either hit them or attack them in a figurative way, especially through angry words.